The group, backed by senior Tory Eurosceptics Michael Gove and Boris Johnson, beat off a challenge from Grassroots Out (GO), supported by Ukip leader Nigel Farage.

The Electroral Commission’s decision could be challenged in the courts by Leave.EU, the group founded by businessman and Ukip backer Arron Banks, which supportied GO’s application.

Leave.EU’s head of communications, Andy Wigmore, said: “We believe it is a stitch-up. We were always aware that this might happen, it clearly has happened, and we are going to take counsel’s advice on this.” He warned that the date of the referendum could be delayed.

‘Come together’

His stance was at odds with Mr Farage, who congratulated Vote Leave, saying: “I have always wanted all on the Leave side to come together and have done my best to try and make this happen. I’ll continue to do so in the run up to the referendum to ensure the Leave side wins.

“We in Ukip, as I’ve said from the start, will work with anyone that wants to leave the EU. We must work together to get our country out of the European Union.”

GO campaigner and Tory MP, Peter Bone, said: “We congratulate Vote Leave on securing designation and we thank our supporters for all the hard work they have put into the campaign so far.

“We look forward to working closely and productively with all those who want to see the UK set free to determine its own destiny. We are determined to play our part in creating a united front to secure victory on June 23 for Leave – Independence Day.”

Britain Stronger In Europe, backed by David Cameron and chaired by former Marks and Spencer boss Stuart Rose, was the only one applicant bidding to become the lead campaign for Britain to stay in the EU. It has been designated as such by the Electoral Commission.

Competing applicants

Claire Bassett, chief executive of the Electoral Commission said: “Where there are competing applicants for a particular outcome, the law is clear – we must designate the applicant which appears to us to represent those campaigning for that outcome to the greatest extent.

“After careful consideration, the Commission decided that ‘Vote Leave Ltd’ better demonstrated that it has the structures in place to ensure the views of other campaigners are represented in the delivery of its campaign.”

Like Britain Stronger In Europe, Vote Leave will now be able to spend up to £7m in the build-up to the 23 June poll, with other registered out campaigners limited to £700,000. It will also have access to a grant of up to £600,000, free mailshots and guaranteed TV broadcasts.

A spokesman for Vote Leave said: “Our focus has always been the real campaign and the £350m we send to Brussels every week, which we want to spend on our priorities like the NHS. We will continue to work constructively with everyone who wants to campaign for a Leave vote.”

Mr Cameron tweeted: “Congratulations to @StrongerIn who have been designated as the Remain campaign in the EU referendum. We’re stronger, safer and better off in.”